The North has halted missile and nuclear tests during previous talks, only to resume them when it lost patience or felt it was not getting what it demanded, analysts say.

Some expressed concern the Trump regime could "fall into the North Korean trap" of granting concessions with nothing tangible in return.

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Media captionThe South's Chung Eui-yong talks to reporters at the White House

Later, White House spokesperson Sarah Sanders said the president would demand "concrete steps and concrete actions" from North Korea before any meeting took place.

She did not specify what those steps were, nor repeat previous assertions that the meeting would take place by May.

There has been no mention of the developments as yet on North Korean state media.

In Sweden, meanwhile, local diplomatic sources were quoted as saying the North's Foreign Minister Ri Yong-ho would be visiting his Swedish counterpart soon.

The Swedish embassy in Pyongyang represents US, Canadian and Australian diplomatic interests there.

Moon's huge gamble

Analysis by the BBC's Laura Bicker in Seoul

South Korean President Moon Jae-in has acknowledged there are obstacles ahead. He is managing expectations and so much can go wrong.

His approval ratings took a hit during the Winter Olympics after he integrated the women's hockey team with players from the North and met a general from Pyongyang who had been accused of masterminding deadly attacks on South Koreans, though they have since rebounded.

These talks are a huge gamble with a communist state which is hard to read.

But if, just if, he helps pull it off, it may reduce the threat of nuclear war and he could win himself a Nobel Peace Prize.

Image copyrightAFPImage caption
North Korean cheerleaders with a unified Korean flag at the Winter Olympics

Speaking outside the White House after the meeting, South Korean National Security Adviser Chung Eui-yong said Mr Kim was prepared to sit down with the US president and was now "committed to denuclearisation".

But Senator Lindsey Graham told the same news outlet that although he was "not naive", President Trump's "strong stand against North Korea and its nuclear aggression gives us the best hope in decades to resolve this threat peacefully".